Verifying IP Multicast Operation

This module describes how to verify IP multicast operation in a network after Protocol Independent Multicast (PIM) sparse mode (PIM-SM) or Source Specific Multicast (PIM-SSM) has been implemented. The tasks in this module can be used to test IP multicast reachability and to confirm that receivers and sources are operating as expected in an IP multicast network.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Prerequisites for Verifying IP Multicast Operation

Before performing the tasks in this module, you should be familiar with the concepts described in the “ IP Multicast Technology Overview ” module.

The tasks in this module assume that IP multicast has been enabled and that PIM-SM or SSM has been configured using the relevant tasks described in the “ Configuring Basic IP Multicast ” module.

Restrictions for Verifying IP Multicast Operation

For PIM-SM, this module assumes that the shortest path tree (SPT) threshold for PIM-enabled routers is set to the value of zero (the default) and not infinity. For more information about setting the SPT threshold, see the ippimspt-threshold command page in the Cisco IOS IP Multicast Command Reference.

Verifying IP multicast operation in a bidirectional PIM (bidir-PIM) network or a PIM-SM network with a finite or infinite SPT threshold is outside the scope of this module.

Information About Verifying IP Multicast Operation

Guidelines for Verifying IP Multicast Operation in a PIM-SM and PIM-SSM Network Environment

When you verify the operation of IP multicast in a PIM-SM network environment or in an PIM-SSM network environment, a useful approach is to begin the verification process on the last hop router, and then continue the verification process on the routers along the SPT until the first hop router has been reached. The goal of the verification is to ensure that IP multicast traffic is being routed properly through an IP multicast network.

How to Verify IP Multicast Operation

Using PIM-Enabled Routers to Test IP Multicast Reachability

Perform the following tasks to use PIM-enabled routers to test IP multicast reachability.

If all the PIM-enabled routers and access servers that you administer are members of a multicast group, pinging that group causes all routers to respond, which can be a useful administrative and debugging tool.

To use PIM-enabled routers to test IP multicast reachability, perform the following tasks:

Configuring Routers to Respond to Multicast Pings

Perform the following task to configure routers to respond to multicast pings. Performing this task configures interfaces on the router to join a specified group. This task should be performed on each interface on the router participating in the multicast network and on all routers participating in the multicast network.

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacetypenumber

4.ipigmpjoin-groupgroup-address

5. Repeat Step 3 and Step 4 for each interface on the router participating in the multicast network.

6.end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacetypenumber

Example:

Router(config)# interface gigabitethernet 1/0/0

Enters interface configuration mode.

For the type and number arguments, specify an interface that is directly connected to hosts or is facing hosts.

Step 4

ipigmpjoin-groupgroup-address

Example:

Router(config-if)# ip igmp join-group 225.2.2.2

(Optional) Configures an interface on the router to join the specified group.

For the purpose of this task, configure the same group address for the group-address argument on all interfaces on the router participating in the multicast network.

Note

With this method, the router accepts the multicast packets in addition to forwarding them. Accepting the multicast packets prevents the router from fast switching.

Step 5

Repeat Step 3 and Step 4 for each interface on the router participating in the multicast network.

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Step 6

end

Example:

Router(config-if)# end

Ends the current configuration session and returns to privileged EXEC mode.

Pinging Routers Configured to Respond to Multicast Pings

Perform the following task on a router to initiate a ping test to the routers configured to respond to multicast pings. This task is used to test IP multicast reachability in a network.

SUMMARY STEPS

1.enable

2.pinggroup-address

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

pinggroup-address

Example:

Router# ping 225.2.2.2

Pings an IP multicast group address.

A successful response indicates that the group address is functioning.

Verifying IP Multicast Operation in a PIM-SM or a PIM-SSM Network

Perform the following optional tasks to verify IP multicast operation in a PIM-SM or a PIM-SSM network. You can perform the steps in these tasks to locate a faulty hop when sources and receivers are not operating as expected.

Note

If packets are not reaching their expected destinations, you might want consider disabling IP multicast fast switching, which would place the router in process switching mode. If packets begin reaching their proper destinations after IP multicast fast switching has been disabled, then the issue most likely was related to IP multicast fast switching. See the “ Monitoring and Maintaining IP Multicast ” module for information on how to disable IP multicast fast switching.

To verify IP multicast operation in a PIM-SM or PIM-SSM multicast network, perform the following verification tasks:

Verifying IP Multicast Operation on the Last Hop Router

Perform the following task to verify the operation of IP multicast on the last hop router.

Note

If you are verifying a last hop router in a PIM-SSM network, ignore Step 3.

SUMMARY STEPS

1.enable

2.showipigmpgroups

3.showippimrpmapping

4.showipmroute

5.showipinterface [typenumber]

6.showipmfib

7.showippiminterfacecount

8.showipmroutecount

9.showipmrouteactive[kb/s]

DETAILED STEPS

Step 1

enable

Enables privileged EXEC mode. Enter your password if prompted.

Router> enable

Step 2

showipigmpgroups

Use this command to verify IGMP memberships on the last hop router. This information will confirm the multicast groups with receivers that are directly connected to the last hop router and that are learned through IGMP.

Use this command to confirm that the group-to-RP mappings are being populated correctly on the last hop router.

Note

Ignore this step if you are verifying a last hop router in a PIM-SSM network. The showippimrpmappingcommand does not work with routers in a PIM-SSM network because PIM-SSM does not use RPs. In addition, if configured correctly, PIM-SSM groups should not appear in the output of the showippimrpmappingcommand.

Use this command on the last hop router to display information about active multicast sources sending traffic to groups on the last hop router. The output of this command provides information about the multicast packet rate for active sources.

Note

By default, the output of the showipmroute command with the active keyword displays information about active sources sending traffic to groups at a rate greater than or equal to 4 kb/s. To display information about active sources sending low-rate traffic to groups (that is, traffic less than 4 kb/s), specify a value of 1 for the kb/s argument. Specifying a value of 1 for this argument displays information about active sources sending traffic to groups at a rate equal to or greater than 1 kb/s, which effectively displays information about all possible active source traffic.

The following is sample output from the showipmroutecommand with the active keyword:

Use this command on routers along the SPT to display information about active multicast sources sending to groups. The output of this command provides information about the multicast packet rate for active sources.

Note

By default, the output of the showipmroute command with the active keyword displays information about active sources sending traffic to groups at a rate greater than or equal to 4 kb/s. To display information about active sources sending low-rate traffic to groups (that is, traffic less than 4 kb/s), specify a value of 1 for the kb/s argument. Specifying a value of 1 for this argument displays information about active sources sending traffic to groups at a rate equal to or greater than 1 kb/s, which effectively displays information about all possible active source traffic.

The following is sample output from theshowipmroute command with the active keyword:

Use this command on the first hop router to display information about active multicast sources sending to groups. The output of this command provides information about the multicast packet rate for active sources.

Note

By default, the output of the showipmroute command with the active keyword displays information about active sources sending traffic to groups at a rate greater than or equal to 4 kb/s. To display information about active sources sending low-rate traffic to groups (that is, traffic less than 4 kb/s), specify a value of 1 for the kb/s argument. Specifying a value of 1 for this argument displays information about active sources sending traffic to groups at a rate equal to or greater than 1 kb/s, which effectively displays information about all possible active source traffic.

The following is sample output from theshowipmroute command with the active keyword:

Verifying IP Multicast on the Last Hop Router Example

The following is sample output from the showipigmpgroups command. The sample output displays the IGMP memberships on the last hop router shown in the figure. This command is used in this example to confirm that the IGMP cache is being properly populated for the groups that receivers on the LAN have joined.

The following is sample output from the showippimrpmappingcommand. In the sample output, notice the RP address displayed for the RP field. Use the RP address and group information to verify that the group-to-RP mappings have been properly populated on the last hop router shown in the figure.

Note

In the output, the “(?)” indicates that the router is unable to resolve an IP address to a hostname.

The following is sample output from theshowipmroute command. This command is used to verify that the mroute table is being properly populated on the last hop router shown in the figure. In the sample output, notice the T flag for the (10.0.0.1, 239.1.2.3) mroute. The T flag indicates that the SPT-bit has been set, which means a multicast packet was received on the SPT tree for this particular mroute. In addition, the RPF nbr field should point toward the RPF neighbor with the highest IP address determined by unicast routing toward the multicast source.

The following is sample output from the showipinterface command for the incoming interface. This command is used in this example to confirm that IP multicast fast switching is enabled on the last hop router shown in the figure. When IP multicast fast switching is enabled, the line “IP multicast fast switching is enabled” displays in the output.

The following is sample output from theshowippiminterfacecount command. This command is used in this example to confirm that multicast traffic is being forwarded to the last hop router shown in the figure. In the sample output, notice the Mpackets In/Out field. This field displays the number of multicast packets received by and sent on each interface listed in the output.

The following is sample output from the showipmroutecommand with the count keyword. This command is used on the last hop router shown in the figure to verify the packets being sent to groups from active sources. In the sample output, notice the packet count displayed for the Forwarding field. This field displays the packet forwarding count for sources sending to groups.

The following is sample output from the showipmroutecommand with the active keyword. This command is used on the last hop router shown in the figure to confirm the multicast groups with active sources on the last hop router.

Note

In the output, the “(?)” indicates that the router is unable to resolve an IP address to a hostname.

Verifying IP Multicast on Routers Along the SPT Example

The following is sample output from the showipmroutefor a particular group. This command is used in this example to verify that the RPF neighbor toward the source is the expected RPF neighbor for the router along the SPT shown in the figure.

The following is sample output from theshowipmroute command with the active keyword from the router along the SPT shown in the figure. This command is used to confirm the multicast groups with active sources on this router.

Note

In the output, the “(?)” indicates that the router is unable to resolve an IP address to a hostname.

Verifying IP Multicast on the First Hop Router Example

The following is sample output from the showipmroutefor a particular group. This command is used in this example to verify the packets being sent to groups from active sources on the first hop router shown in the figure. In the sample output, notice the packet count displayed for the Forwarding field. This field displays the packet forwarding count for sources sending to groups on the first hop router.

Note

The RPF nbr 0.0.0.0 field indicates that the source of an mroute has been reached.

RFCs

No new or modified RFCs are supported, and support for existing RFCs has not been modified.

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Feature Information for Verifying IP Multicast Operation

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Table 4 Feature Information for Verifying IP Multicast Operation

Feature Name

Releases

Feature Information

This table is intentionally left blank because no features were introduced or modified in this module since Cisco IOS XE Release 2(1). This table will be updated when feature information is added to this module.